1. Technical Field
The invention relates to apparatus and methods for bending and pressing into curved shaped workpieces having a plurality of layers. More specifically, the invention relates to an apparatus and method for bending and pressing laminations into 2-dimensional or 3-dimensional curves without using a mold, form or adjustable jig.
2. Discussion of the Prior Art
Curved wood forms having circular, oval, hyperbolic, elliptical or similar shapes may be achieved by the steam bending of solid wood, or by bending a stack of laminates and intermediate glue into a desired shape. Laminated curved wood parts are usually preferred over curved parts made of solid wood, since they are of superior strength and stability. Furthermore, unset laminates generally require less bending force than solid wood parts. However, to achieve a satisfactory curved wood part, the laminates must not only be bent, but must also be held after bending in the exact position and shape desired until the glue or adhesive is set or cured. In addition, substantial pressure must be applied to compress the laminations of a workpiece during the setting of the glue and the created pressure must be evenly distributed along the workpiece to achieve a bent laminate of uniform consistency and quality. A number of prior art apparatus and methods have been proposed for the bending of unset laminates, however, these apparatus are expensive, difficult to adjust to different curvatures, not applicable for the production of two dimensional as well as three dimensional curvatures, or require specific molds or patterns for each size and shape of curvature to be produced.
German published application DE 2,251,497 by Mayer teaches an apparatus for the manufacture of laminated handrails for spiral stairs. The apparatus includes a vertical post and a number of horizontal braces which represent the steps of a spiral staircase. Each horizontal brace has a sleeve, which is guided along the post and is affixed to one subunit of a folding steel trellis. The top and bottom sleeves include an interior thread which engages a complementary thread on the post. Rotation of the post increases or decreases the length of the foldable steel trellis so that any height and rising angle of the spiral staircase can be adjusted. The apparatus further includes vertical brackets, which are slidably mounted on the horizontal braces for adjustment of the radius of the handrail. The unset handrail laminate is positioned along the outside of the vertical brackets and pressed against the brackets by a steel plate tensioned along the outside of the laminate. Thus, time consuming adjustment of both the horizontal braces and the vertical brackets is required for the achievement of a handrail of a different radius or rise and run. Furthermore, the published application does not teach the production of 2-dimensional curvatures.
The same applies to the apparatus described in German published application DE 1,728,013 also by Mayer. This apparatus is of the same basic construction as the one disclosed in DE 2,251,497 except that the sleeves are not freely slidable along a vertical post but are all threaded and each engage a complementary thread extending the whole length of the post.
U.S. Pat. No. 3,902,948 by Morros discloses an apparatus similar in construction to the apparatus discussed above, which is used for the forming of stringers of curved stairways. The stringer is formed by placing a stack of pre-glued laminations in a pair of holding brackets mounted on each of a number of horizontal beams, which are carried by a vertical central post and represent the steps of the stairway. A stiffener board is placed along the stack of laminates and in the holding brackets. Air tubes are positioned between the laminates and the stiffener board and are inflated to press the laminations together. Again, time consuming adjustment is required for the production of stringers of different radii or rise and run. Also, the assembly time of the laminates in the apparatus together with the stiffener board and the air tubes is unsatisfactory.
U.S. Pat. No. 4,886,568 by Strozier teaches an adjustable radius wood laminate bending and gluing fixture, for the bending and compressing of a stack of laminations and adhesive between two flexible bands that are drawn against adjustably positioned stanchions. The position of the stanchions in radial slots in a bed defines the desired curve for the workpiece. The bands are tensioned by cables, which pass through appropriate pulleys and attach to the band ends. However, in order to adjust the fixture to different radii, the stanchions must be moved.
U.S. Pat. No. 4,909,889 by Strozier discloses a wood laminate bending apparatus wherein laminations are drawn against curve-defining plates or patterns by a belt of adjustable length, which is attached to a rack and is tensioned by movement of the rack away from the plates or patterns. The curve-defining plates or patterns are interchangeable but each provide only one specific curvature. Other laminate bending and gluing apparatus are disclosed in U.S. Pat. Nos. 1,954,183; 3,205,110; 4,089,732; DE 3,046,088; GB 1,391,077 and GB 1,391,078.
Thus, an apparatus is desired which is easily adaptable to different shapes and sizes of 2- and 3-dimensional curvatures and permits the fast and economical bending of a workpiece having individual layers.